1. Field of the Invention
This invention relates generally to encryption. More specifically, this invention relates to implementing a soft key for use with a hard encryption core in programmable logic devices and similar configurable devices.
2. Description of Related Art
A programmable logic device (PLD) is a programmable integrated circuit that allows the user of the circuit, using software control, to customize the logic functions the circuit will perform. Programmable logic devices supplied by integrated circuit manufacturers like Altera Corporation of San Jose, Calif. are not inherently capable of performing any specific function. The user, in conjunction with software supplied by the PLD manufacturer, can program the PLD to perform the specific function or functions required by the user's application. The PLD then can function like a dedicated logic chip.
A typical PLD consists of an array of logic cells that can be individually programmed and interconnected to each other to provide internal input and output signals, thus permitting the performance of highly complex combinational and sequential logic functions. Users typically prepare electronic designs for a PLD using electronic design automation (EDA) software tools, usually provided by the chip vendor, to do technology mapping, partitioning and placement, routing and binary configuration data output generation. The resulting binary configuration data (representing the electronic design) can be programmed into a ROM connected to the PLD or downloaded to the PLD from a connected computer.
By the time the electronic design is created, it typically represents significant time, money and effort. To encourage individuals and companies to continue to invest in the research and development of new electronic designs, and to protect the investment represented by existing completed designs, it is desirable to provide some method of protecting the electronic designs from illegal or otherwise unauthorized copying or use, which has become a more acute problem in the field.
To make an illegal copy of the electronic design intended for a PLD, one need only make a copy of the binary configuration data. This can be done by copying the bit stream transmitted externally between the PLD and the device installing the configuration data, and then using the copied bit stream with a similar PLD. Thus, the copied electronic design can be illegally used with other programmable devices. It therefore is desirable to make it as difficult as possible to copy the binary configuration data that represents the electronic design.
Several techniques have been developed to address the illegal copying of programmable device electronic designs by users of PLDs. The goal of these techniques is to make it impossible (or at least much more difficult) to illegally copy electronic designs and other proprietary information or data. While these efforts have met with some success, they have some shortcomings. For example, some security mechanisms (e.g., encryption algorithms) have been implemented in soft logic where they are more susceptible to attack by reverse engineering from the exposed pins of the programmable device. As such, the binary configuration data can be modified to either remove a disable signal or to change the key to the encryption algorithm.
A technique that permits full use of an electronic design while protecting the proprietary interests of the owners of the intellectual property incorporated in such a design would represent a significant advancement in the art.